crosperf: fix lint warnings.

BUG=chromium:570454
TEST=the lint warning is gone, unittest still passes.

Change-Id: Icdb9c0ba6ecdd7a04bec8eafc96f84813e59b583
Reviewed-on: https://chrome-internal-review.googlesource.com/243139
Commit-Ready: Yunlian Jiang <yunlian@google.com>
Tested-by: Yunlian Jiang <yunlian@google.com>
Reviewed-by: Luis Lozano <llozano@chromium.org>
1 file changed